The present invention relates to a method of applying a protective boron nitride (BN) film to quartz.
In order to obtain desired electrical properties in solid state devices, the composition of semiconductor materials from which the devices are fabricated is carefully controlled and maintained free of contaminants. Frequently, semiconductor materials are prepared by conventional liquid epitaxial growth methods (described more fully hereinafter) wherein molten semiconductor material is held in a crucible positioned within a quartz tube disposed in a furnace. It has been found, however, that due to high temperatures involved, the semiconductor material may be contaminated by silicon derived from the quartz tube. Such contamination renders materials such as gallium phosphide (GaP) and gallium arsenide (GaAs), for example, unsuitable for fabricating light-emitting diodes and power transistors, respectively.
In the past, one approach employed to minimize silicon contamination of semiconductor material has been to machine from sintered BN a tubular member, which when inserted into the aforementioned quartz tube, provides a silicon impermeable barrier between the semiconductor material and the quartz tube. This approach is generally unsatisfactory because the separate BN member is expensive to manufacture, does not entirely avoid contamination, and does not protect quartz from attack by acids used to cleanse the apparatus.
The present invention provides a method for directly coating quartz with a protective BN film, which forms an integral structure with the quartz. The inventive method provides a coating which is economical to fabricate, protects quartz from acid attack, and provides superior resistance to thermal shock. Since the BN film adheres tightly to quartz, superior protection from silicon contamination of the semiconductor material is also provided.